1. Field of the Invention
This invention relates to a process for the production of concentrated mono- and/or disalt dispersions of .alpha.-sulfofatty acids by sulfonation of saturated fatty acids and/or fatty acid mixtures with sulfur trioxide, anionic and/or nonionic surfactants being added during the neutralization stage to improve the flowability of the dispersions. The invention also relates to the concentrated dispersions of .alpha.-sulfofatty acid mono- and/or disalts obtainable by this process.
2. Discussion of Related Art
The production of .alpha.-sulfofatty acid disalts, hereinafter referred to in short as disalts, by sulfonation of fatty acids is known per se from the literature. According to U.S. Pat. No. 1,926,442 for example, saturated carboxylic acids can be converted into .alpha.-sulfofatty acid disalts by reaction with strong sulfonating agents under drastic reaction conditions. Sulfur trioxide, oleum and chlorosulfonic acid are described as suitable sulfonating reagents. If the acidic sulfonation products accumulating during the sulfonation reaction are only partly neutralized, .alpha.-sulfofatty acid monosalts, hereinafter referred to in short as monosalts, are obtained.
In addition, it is known that disalts based on C.sub.16-18 fatty acids are distinguished by good detergency properties, cf. in particular applicants' European patents EP 112 291 and EP 112 292.
Because monosalts can be readily converted into the corresponding disalts, for example by direct neutralization or, where they are used in detergent formulations, indirectly by the alkalinity of a detergent slurry, monosalts are also extremely important surfactants for detergents.
In practice, anionic surfactants are often used in the form of concentrated, flowable aqueous pastes in subsequent applications. Accordingly, there is a need for concentrated, flowable mono- and/or disalt pastes. Hitherto, however, concentrated and flowable mono- and disalt pastes have not been readily obtainable because the aqueous mono- and/or disalt pastes obtained in the industrial sulfonation of saturated fatty acids after partial or complete neutralization are extremely viscous above a concentration of 20 to 30% by weight and can no longer be pumped.
There is a connection between the increase in the viscosity of aqueous mono- and disalt pastes with increasing content of mono- and/or disalt in the pastes and the poor solubility of these surfactants in water. Literature data are set out in Tables 1 and 2.
TABLE 1 ______________________________________ Solubility of .alpha.-sulfofatty acid salts in water at 30.degree. C. in % by weight Cation C.sub.16 Mono- C.sub.16 Di- C.sub.18 Mono- C.sub.18 Di- Lit. ______________________________________ Lithium &gt;5 0.3 &gt;5 1 Sodium 0.07 0.34 0.05 1 Potassium 0.04 0.49 1 Magnesium 0.06 &gt;5 &lt;0.01 1 Calcium 0.28 0.03 1 Ammonium 0.2 0.7 0.05 1+2 Sodium 0.1 2 ammonium ______________________________________ Lit. 1: J. K. Weil, R. G. Bistline Jr., A. J. Stirton; J. Am. Oil Chem. Soc. 1957 (34) 100 Lit. 2: J. K. Weil, A. J. Stirton, E. W. Maurer, W. C. Ault, W. E. Palm; J. Am. Oil Chem. Soc. 1958 (35) 461
TABLE 2 ______________________________________ Solubility of .alpha.-sulfofatty acid salts in water at 40.degree. C. in % by weight. Cation Type C.sub.12 C.sub.14 C.sub.16 C.sub.18 Lit. ______________________________________ Sodium Mono- 0.74 0.17 0.10 0.05 3 Sodium Di- 7.4 1.5 0.45 0.14 3 Ammonium Mono- 0.50 3 ______________________________________ Lit. 3: A. J. Stirton, J. K. Weil; Surfactant Sci. Ser., Volume 2, Part 2 "Anionic Surfactants", page 388, Marcel Dekker 1976.
The problem of an industrially useful process for the production of concentrated, flowable aqueous mono- and/or disalt dispersions has not yet been satisfactorily solved by the prior art.
Accordingly, the problem addressed by the present invention was to provide an industrial process for the production of concentrated, flowable mono- and/or disalt dispersions starting out from the sulfonation of saturated fatty acids with gaseous SO.sub.3.